1. Field of the Invention
The present invention relates to antennas for card devices loadable into electronic apparatuses, such as personal computers.
2. Background Art
FIG. 6 is a simplified schematic diagram illustrating an example of a card device. A card device 41 includes a card casing 42, a circuit substrate 43 housed inside the card casing 42, and an antenna 44 disposed rotatably on the exterior of the card casing 42.
The base end of the antenna 44 is provided with an antenna rotary shaft 45 composed of a conductive material. One side wall of the card casing 42 is provided with a through hole (not numbered) through which the antenna rotary shaft 45 extends from the exterior to the interior of the card casing 42. The antenna rotary shaft 45 extending into the card casing 42 through this through hole is electrically connected to an electric circuit (not shown) disposed on the circuit substrate 43. Accordingly, the antenna 44 is electrically connected to the electric circuit on the circuit substrate 43 via the antenna rotary shaft 45.
Two patent documents of background interest are:
(Patent Document 1) Japanese Unexamined Patent Application Publication No. 2001-339211; and
(Patent Document 2) Japanese Unexamined Patent Application Publication No. 2002-374111.
Because the antenna rotary shaft 45 is rotatable, it is not desirable to connect the antenna rotary shaft 45 directly to the circuit substrate 43 due to various problems that may be caused by the rotation of the antenna rotary shaft 45. Accordingly, as shown in a schematic cross-sectional view in FIG. 7, the antenna rotary shaft 45 is electrically connected to the electric circuit on the circuit substrate 43 via a feeding terminal 46 (for example, see Patent Document 1).
In the example shown in FIG. 7, the feeding terminal 46 is composed of a conductive material and includes an antenna-rotary-shaft connection part 46A that is in contact with the antenna rotary shaft 45, and a circuit connection part 46B that is in contact with an antenna connection land 47 of the electric circuit, which is disposed on a substrate surface of the circuit substrate 43. Since the antenna rotary shaft 45 is in contact with the antenna-rotary-shaft connection part 46A of the feeding terminal 46 and the circuit connection part 46B of the feeding terminal 46 is in contact with the antenna connection land 47 of the circuit substrate 43, the antenna 44 is electrically connected to the electric circuit of the circuit substrate 43 via the antenna rotary shaft 45 and the feeding terminal 46. Reference numeral 48 in FIG. 7 indicates a wiring pattern for connecting the antenna connection land 47 to, for example, a radio-communication high-frequency circuit (not shown) in the electric circuit.
If the antenna rotary shaft 45 is electrically connected to the electric circuit of the circuit substrate 43 via the feeding terminal 46 as shown in FIG. 7, the following problems may exist. Specifically, when the circuit substrate 43 is viewed from above, the feeding terminal 46 has a configuration in which the part 46A in contact with the antenna rotary shaft 45 and the part 46B in contact with the antenna connection land 47 of the circuit substrate 43 are disposed side-by-side, in parallel. Furthermore, in view of preventing a connection failure between the antenna rotary shaft 45 and the antenna connection land 47, it is not desirable to reduce the size of the antenna-rotary-shaft connection part 46A and the circuit connection part 46B. For these reasons, it is difficult to reduce the area occupied by the feeding terminal 46 on the card device 41.
Furthermore, a signal transferred between the antenna 44 and the electric circuit of the circuit substrate 43 must travel through two contact points, namely, the contact point between the antenna-rotary-shaft connection part 46A of the feeding terminal 46 and the antenna rotary shaft 45, and the contact point between the circuit connection part 46B of the feeding terminal 46 and the antenna connection land 47 of the circuit substrate 43. Since the two conductors are only in contact with each other at each of these contact points, the signal may easily be subject to a conduction failure. Moreover, this may also be problematic in inducing a large conduction loss of the signal. These problems may possibly result in lower reliability of the radio communication performance of the card device 41. On the other hand, gold-plating the surface of the antenna connection land 47, for example, to enhance the reliability of the contact between the feeding terminal 46 and the antenna connection land 47 can lead to higher costs.